The goal of this project is to better understand the historian's functioning and impact as an expert witness. An expert witness historian testifies in court to help the judge and the jury understand complex historical matters that are relevant to a case. Historical testimony plays a pivotal role in cases in which the historical consciousness of manufacturers and the public about the harmful qualities of cigarettes is important. My doctoral research questioned the compatibility of historical research methods and forensic testimony in the U.S. This postdoctoral project adds two distinct layers of analysis. Firstly, I will comparatively analyze how procedural rules in different legal systems determine the impact of forensic historians. Secondly, I will measure the impact of forensic historians on research agendas and cigarette historiography as well as on public information campaigns on tobacco. I will compare legal codes, records of cigarette litigation, formerly confidential cigarette company documents, cigarette historiography, and tobacco control documents in four case studies: Australia, Canada, the Netherlands, and the U.S. after 1980. My analysis will show how forensic historians in different countries have unevenly impacted our knowledge of the history of the global cigarette epidemic. This combined approach is novel and broadens our understanding of the functioning and impact of forensic historians in order to encourage more responsible engagement in such practices.